The apostles were initially doubtful and afraid after Jesus' death, but after His resurrection and spending 40 days teaching them, their understanding of Scripture changed. Jesus opened their minds to understand the prophecies about His suffering and resurrection. He empowered them with the Holy Spirit at Pentecost. Peter and the apostles then boldly preached the gospel, performing signs and wonders. Their teachings were based on what Jesus had taught them from Scripture during the 40 days.